This invention relates to a metallic vapor laser apparatus and more particularly, to a metallic vapor laser apparatus which prolongs the life of the apparatus by reducing the quantity of a metallic vapor for excitation that is lost, reduces the quantity of a buffer gas that is consumed and produces an output having high stability by stable discharge and oscillation.
In the conventional metallic vapor laser apparatus having the construction as shown in FIG. 3 of Japanese Laid-open Patent Publication Sho No. 63-229782(1988), the temperatures of the discharge tube, electrodes, heat-insulating material for high temperature, insulating pipe, etc., rise at the time of laser oscillation. As a result, a binder and metal oxides as a kind of ceramics which are used for shaping the heat-insulating material for high temperature made of fibrous ceramics are exposed to the high temperature and evaporate, so that a gaseous impurity is generated and discharge occurs by the insulating material on the outer periphery of the discharge tube. Part of this discharge diffuses into the inside of the discharge tube, makes an original discharge unstable and reduces discharge resistance with the result being a drop of excitation efficiency due to discharge. Accordingly, in the prior art apparatuses, gaps are defined between the electrodes and the discharge tube, respectively, so as to introduce the gaseous impurity generated by the heat-insulating material for high temperature into the internal space, and at the same time, a gas inlet and a gas outlet are disposed outside the electrodes in the axial direction, respectively. Further, a buffer gas is always supplied and caused to flow into the discharge tube in such a manner as to discharge the gaseous impurity described above outside the discharge tube.
According to the conventional metallic vapor laser apparatus having the construction described above, however, there is the problem that large quantities of copper vapor is also discharged with the gaseous impurity by the buffer gas; moreover, there is also the problem that the consumption quantity of the buffer gas is great. For this reason, consumption of the copper plate 1 is promoted and service life of the metallic vapor laser apparatus is shortened. When the amount of the copper plate becomes small, copper must be supplied; but since the discharge tube in which the copper plate is disposed is under the state where the voltage is as high has about 20 KV and the temperature is at about 1,500.degree. C., it is therefore difficult in practice to supply copper under the state where a laser oscillates. To supply copper, it has been necessary generally to disassemble the laser apparatus, then to supply copper and to assemble once again the laser apparatus. This has been extremely troublesome. Accordingly, the service life of the metallic laser apparatus is practically determined by how the consumption quantity of the copper plate is reduced. At present, the service life of the metallic vapor laser apparatus is about 100 hours. The life of this extent is sufficient as an experimental apparatus but since the laser apparatus is continuously used day and night in a practical operation such as enrichment of uranium, it is not possible to put the conventional metallic vapor laser apparatus into practical use. Even if the laser apparatus is constituted in such a manner as to disassemble it and then to supply copper, hundreds of laser apparatuses are used for uranium enrichment and each apparatus must be disassembled per a few minutes to supply the copper plate. For this reason, practical utilization is difficult even according to this construction. As described above, the supply of the copper plate for generating the metallic vapor inside the internal space of the discharge tube or the reduction of its consumption quantity is an extremely critical problem for the practical utilization of the metallic vapor laser apparatus.